REMOT- 


)RAGE 


[Reprinted  from  Biological  Bulletin,  Vol.  IX.,  No.  6,  November,  IQ05.] 


OBSERVATIONS  ON  THE  PROGENY  OF 
VIRGIN  ANTS. 

ADELE  M.  FIELDE. 

The  value  of  the  experimental  work  here  presented  lies  mainly 
in  the  complete  protection  of  the  virginity  of  the  ant-mothers 
during  their  whole  lifetime,  or  from  their  pupa-stage  to  the  close 
of  the  experiments  undertaken  with  them,  and  in  the  perfect 
safeguarding  of  their  eggs  from  contact  with  spermatozoa  out- 
side the  body  of  the  ant. 

At  the  present  time,  so  far  as  is  known  to  the  writer,  published 
observations  on  the  offspring  of  worker  ants  may  be  placed  in 
three  categories.  Those  in  the  first  category  present  a possibility 
that  a queen’s  eggs  were  inadvertently  included  in  the  nest  with 
the  workers  sequestered.  When  ants  are  transferred  from  a 
natural  to  an  artificial  nest,  it  often  happens  that  eggs,  unobserved 
at  the  time  of  sequestration,  are  discovered  in  the  new  nest  within 
a few  days  thereafter.  Ants  are  tenacious  of  their  charges,  and 
they  sometimes  conceal  eggs  or  small  larvae  in  their  mouths,  or 
carry  them  adhering  to  their  persons.  In  this  way  eggs  may  be 
unwittingly  transferred  to  the  new  abode  and  may  afterward  be 
brought  together  in  a pile  or  packet,  the  observer  believing  them 
to  be  the  product  of  the  worker-ants  when  they  are  really  the 
issue  of  a queen  in  the  old  habitation.  Unless  the  ants  were 
^singly  and  carefully  examined  and  freed  from  adherent  eggs,  or 
unless  a longer  time  than  the  twenty  days  ordinarily  required  for 
incubation  has  elapsed  since  the  segregation  of  the  workers, 
there  is  reason  for  suspecting  that  the  eggs  may  have  been  de- 
posited by  other  ants  than  the  sequestered  ones. 

In  a second  category  may  be  included  all  those  cases  in  which 
larvae  were  intentionally  introduced  among  the  segregated  ants. 
Such  larvae  may  not  have  reached  the  pupa-stage  sooner  than 
the  issue  from  eggs  deposited  in  the  new  nest,  and  it  is  im- 
possible to  maintain  that  the  older  and  the  younger  larvae  are 
always  distinguishable.  I have  had,  in  my  artificial  nests,  larvae 
of  Cremastogaster  lineolata , scarcely  larger  than  the  eggs  from 

355 


356 


ADELE  M.  FIELDE. 


which  they  emerged,  remaining  for  many  months  without  visi- 
ble growth,  and  then  developing  simultaneously  with  the  issue 
of  eggs  deposited  a half  year  later.  1 am  informed  by  Dr.  J. 
H.  McGregor  that  larvae  of  Camponotus  americanus  have  re- 
mained such  during  ten  months  in  his  artificial  nests  at  Columbia 
University  ; and  by  Dr.  I.  A.  Field  that  larvae  of  Camponotus 
pennsylvanicus  remained  under  his  observation  in  apparent  good 
health  and  without  visible  growth  for  nearly  fifteen  months. 
Admitting  that  certain  eggs  were  deposited  by  workers,  we  still 
lack  assurance  that  introduced  larvae  were  not  mingled  with  their 
issue,  and  thus  there  is  created  a reasonable  doubt  as  to  the 
origin  of  the  callows  appearing  in  the  nest  at  a later  date. 

To  a third  category  we  may  relegate  the  numerous  accounts, 
including  my  own,  concerning  the  offspring  of  workers  that  had 
previously  lived  with  males,  and  also  those  accounts  in  which 
male  ants  were  hatched  and  permitted  to  remain  within  the 
segregated  group  of  workers.  We  know  that  ants  sometimes 
mate  within  the  nest,  and  we  have  the  results  of  many  dissections 
indicating  the  capacity  of  certain  workers  for  impregnation. 
Miss  Holliday  1 found  not  only  ovaries  but  a seminal  receptacle 
in  certain  individuals  representing  three  genera  of  ponerine,  two 
genera  of  myrmicine,  and  one  species  of  camponotine  workers, 
none  of  whom  was  externally  distinguishable  from  its  fellows. 
We  can  no  longer  consider  the  workers  of  all  species  of  ants  as 
sterile  females.  In  view  of  the  evidence  that  among  workers, 
showing  no  difference  in  external  structure  there  have  been  found, 
in  numerous  species,  many  members  with  both  ovaries  and  semi- 
nal receptacles  ; and  of  the  testimony  of  competent  witnesses 
that  the  male  ants  sometimes  pursue  the  workers  with  an  ardor 
equal  to  that  shown  in  their  pursuit  of  the  queens,  we  must 
abandon  the  long  cherished  notion  that  eggs  deposited  by  worker 
ants  are  always  unimpregnated. 

We  do  not  know  even  that  ant-eggs  may  not  be  fecundated 
outside  the  body  of  the  female,  and  this  possibility  should  not  be 
ignored  in  cases  where  the  egg-piles  are  traversed  by  mature 
males  in  pursuit  of  queens  and  workers. 

1 “A  Study  of  some  Ergatogynic  Ants,”  Margaret  Holliday.  Contribution  from 
the  Zoological  Laboratory  of  the  University  of  Texas,  June,  1902. 


OBSERVATIONS  ON  THE  PROGENY  OF  VIRGIN  ANTS.  357 

The  absence  of  indubitable  proof  that  the  unfecundated  ant- 
egg  produces  either  male  or  female  ant  impelled  me  to  undertake 
the  formation  of  ant-groups  in  which  no  member  had  ever  lived 
with  a male,  and  from  whose  abode  males  were  excluded.  In 
the  summer  of  1904  I sequestered  pupae,  with  two  or  three 
workers  to  take  care  of  them,  in  artificial  nests  in  which  there 
were  neither  queens  nor  males,  and  as  soon  as  these  pupae 
hatched  I segregated  the  callows  in  new  nests  into  which  no  egg, 
larva  or  pupa  was  ever  introduced.  My  ant-groups  were  thus 
made  up  of  workers  indubitably  virgin,  and  the  eggs  deposited  in 
their  nests  were  certainly  unimpregnated. 

Group  A.  Camponotus  pictus. 

Group  A consisted  of  thirty  workers,  majors  and  minors,  of 
Camponotiis  herculeanus  pictus , hatched  between  July  11  and  31, 

1904,  and  kept  in  segregation  from  their  hatching  until  October, 

1905.  Their  first  eggs,  ten  in  number,  were  deposited  between 
May  14  and  18,  1905,  and  these  had  increased  to  about  fifty  on 
June  4.  The  first  larva  appeared  on  June  6,  nineteen  days  after 
the  first  eggs  were  observed.  On  July  7 the  larvae  had  made 
notable  progress  in  number  and  in  size,  the  largest  then  being  as 
long  as  an  adult  worker.  The  first  cocoon  was  spun  on  July  16, 
and  the  first  offspring  of  these  segregated  virgin  workers  appeared 
on  August  14.  Between  August  14  and  September  30  their 
cocoons  gave  forth  thirty-two  notably  large  and  sturdy  males. 
That  no  female  might  escape  observation  if  hatched  from  these 
cocoons,  the  cocoons  were  transferred,  soon  after  their  formation, 
to  an  annex  of  the  nest  where  only  five  workers  were  admitted. 
Cocoons  and  nurses  were  daily  counted,  and  it  is  certain  no 
queen  nor  worker  ever  hatched  from  these  cocoons. 

Group  B.  Formica  argentata. 

Group  B consisted  of  about  fifty  Formica  argentata  workers, 
all  hatched  from  sequestered  cocoons  during  September,  1904, 
and  kept  in  segregation  by  me  from  the  time  of  hatching  until 
after  the  close  of  this  series  of  observations.  From  eggs  de- 
posited on  July  7,  1905,  the  first  larva  appeared  on  July  19. 
The  first  cocoon  was  spun  on  August  4,  and  the  first  ant  hatched 


358 


ADELE  M.  FIELDE. 


on  August  31.  Only  five  cocoons  were  formed  in  this  nest,  and 
each  of  these  rendered  a large,  fine  male. 

Dr.  Field’s  Group  C.  Formica  argentata. 

Dr.  Irving  A.  Field,  who  simultaneously  with  myself,  seques- 
tered pupae  from  the  same  wild  west  that  provided  my  B 
group,  likewise  segregated  virgin  workers,  to  the  number  of  one 
hundred  and  twenty-five,  all  hatched  between  August  20  and 
September  23,  1904.  From  eggs  laid  between  June  6 and  13, 
1905,  the  first  larva  appeared  on  June  21  ; the  first  cocoon  on 
July  23  ; and  the  first  callow  on  August  7.  All  the  young  pro- 
duced in  this  group  were  males,  of  which  fourteen  had  appeared 
before  September  3,  1905. 

Dr.  Field’s  Group  D.  Formica  pallide-fulva  fuscata. 

This  group,  while  failing  to  meet  prescribed  conditions  in  so  far 
as  the  workers  were  not  sequestered  during  the  whole  of  their 
lives,  is  herein  inserted  because  its  history  is  clearly  recorded. 
It  consisted  of  many  workers,  secured  by  Dr.  Field,  at  Middle- 
sex Fells,  Mass.,  on  March  15,  1904.  The  ants  were  frozen  in 
a mass  when  taken  from  the  ground,  and  every  ant  was  so  care- 
fully examined  before  her  insertion  into  the  artificial  nest  that 
there  is  no  probability  that  eggs  were  introduced  into  the  segre- 
gated group  of  workers.  This  group  remained  under  Dr.  Field’s 
observation  at  Harvard  University.  It  was  placed  in  a chamber 
having  a temperature  of  from  75 0 to  85°  F.  or  from  23 0 to  30° 
C.  On  March  20,  five  days  after  the  sequestration,  the  first  egg 
was  laid  ; on  April  4,  the  first  larva  appeared  ; and  on  April  17, 
the  first  cocoon  was  spun.  Before  June  10,  forty-six  males  had 
appeared  in  this  nest ; and  no  other  than  male  young  had  been 
produced. 

Group  E.  Cremastogaster  lineolata. 

The  progeny  of  a queen  ant  whose  life-experiences  have  all 
been  under  observation,  is  believed  to  be  here  for  the  first  time 
enumerated. 

On  August  18,  1903,  a queen  Cremastogaster  lineolata  hatched 
in  a sequestered  group  of  pupae  in  one  of  my  artificial  nests  1 

1 My  ants  were  under  my  care  at  the  Marine  Biological  Laboratory  at  Woods 
Holl,  Mass.,  during  the  summers,  and  at  my  home  in  New  York  City  during  the  re- 
mainder of  the  year. 


OBSERVATIONS  ON  THE  PROGENY  OF  VIRGIN  ANTS.  359 

and  was  immediately  removed  to  a small  nest,  where  there  were 
several  newly  hatched  workers  and  males  of  Stenamma  fulvam , 
this  group  being  originally  created  for  observation  of  the  behavior 
of  a queen  having  a family  made  up  of  ants  of  other  species 
than  her  own.  When  the  queen  was  but  a few  days  old,  I 
clipped  off  her  wings  to  secure  her  greater  safety  from  accident 
among  the  viscid  food-stuffs  in  the  nest.  During  the  ensuing 
year,  all  the  males  died,  and  three  more  were  hatched  from 
eggs  deposited  by  the  Stenamma  workers.  I did  not  expect 
this  queen  to  lay  eggs,  because  I had  previously  kept  unmated 
queens  (of  Stenamma  fnlvuiri)  a whole  year  without  their  losing 
their  wings  or  depositing  an  egg  during  that  period.  Dr.  Mc- 
Gregor also  kept  winged  queens  (of  Camponoius  americanus)  ten 
months  without  their  losing  their  wings  or  depositing  eggs. 

On  July  31,  1904,  I removed  all  the  Stenammas  from  this  nest, 
cleaned  it  thoroughly,  and  gave  to  the  queen  forty  newly  hatched 
workers  from  her  own  colony,  probably  her  own  sisters.  Three 
days  later  there  were  ten  eggs  in  the  nest,  and  on  August  21 
there  , were  more  than  three  hundred.  That  these  eggs  had  been 
laid  by  the  queen  was  indicated  by  their  size  and  by  the  imma- 
turity of  all  the  workers  in  the  nest.  The  queen  was  eight  milli- 
meters in  length,  the  workers  only  three  to  four  millimeters. 
Moreover,  I compared  the  eggs  with  those  of  an  isolated  queen, 
Cremastogastcr  line  data,  and  found  them  to  match  precisely. 

Young  larvae  were  first  observed  among  the  eggs  on  August 
28  ; the  first  pupa  appeared  on  December  22,  1904,  and  two 
males  hatched  on  January  io,  1905.  These,  when  a day  old, 
were  transferred  to  Dr.  W.  M.  Wheeler  for  expert  examination 
concerning  signs  of  hybridization,  and  were  by  him  reported  to 
be  typical  Cremastogaster  lineolata  males.  Their  successors  in 
the  nest  were  like  them.  No  male  was  permitted  to  mature  in 
the  nest,  all  except  the  first  two  being  removed  before  hatching. 
Before  the  end  of  September,  1905,  sixty-three  males  had  been 
produced  in  this  nest,  the  offspring  of-  this  virgin  queen.  No 
young  queen  or  worker  had  been  seen,  though  the  pupae  in  this 
species  are  always  naked,  and  the  young  had  been  carefully  exam- 
ined at  least  twice  a week. 

While  this  Cremostogaster  lineolata  virgin  queen  was  producing 


360 


ADELE  M.  FIELDE. 


male  offspring  only,  a queen,  Camponotus  pennsylvanicus,  living  in 
a similar  nest  of  mine,  supplied  with  the  same  food,  subject  to 
the  same  daily  temperature,  and  having  about  the  same  number 
of  worker-servants,  produced  numerous  offspring,  exclusively 
female.  The  Camponotus  queen  had  been  captured  when 
dealated,  presumably  after  her  mating.  Although  these  queens 
were  of  different  subfamilies  among  the  ants,  the  similarity  in  all 
the  conditions  of  their  environment  except  the  incident  of  mating, 
points  to  a probability  that  the  sex  of  their  respective  progeny 
was  determined  thereby,  unimpregnated  eggs  producing  males, 
and  impregnated  eggs  producing  females. 

It  is  an  interesting  fact  that  during  the  twenty-six  months  that 
this  Camponotus  pennsylvanicus  queen  remained  under  my  ob- 
servation no  male  appeared  among  the  many  tens  of  her  offspring  ; 
while  eleven  of  her  segregated  daughters  in  the  care  of  Dr.  Field 
produced  at  least  three  male,  and  no  female,  offspring. 

The  observations  here  recorded  establish  the  view  that  some 
virgin  workers  lay  eggs,  and  that  many  ant-eggs  that  have  had 
no  contact  with  spermatozoa  produce  males.  Not  until  female 
progeny  shall  have  been  observed  to  issue  from  eggs  protected 
as  were  those  of  my  Camponotus  pictus  should  we  consider  the 
Dzierzon  theory  inapplicable  to  ants.  No  ant  indisputably 
virgin,  with  her  eggs  perfectly  safeguarded  from  spermatozoa, 
has  yet  presented  evidence  against  the  extension  of  this  theory 
to  the  Formicidae. 

Marine  Biological  Laboratory, 

Wood’s  Holl,  Mass.,  September  1905. 


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